J.C.MacSwell

they didnt' date=' the consensus about universe age is 13.7 or about 14 billion years.

 

expansion started 14 billion Y ago but it started off very fast and was decelerating for the first 9 or 10 billion years

 

then, about 4 or 5 billion Y ago this deceleration stopped and the expansion began to pick up again

 

this means that when you plot the scale factor (loosely called "the size of the universe") the curve has a convex portion and concave portion and an inflection point

 

there should be a picture of that in the SFN Astronomy Reference sticky thread

 

the plot of the scale factor is basically just an increasing ramp showing it getting larger but superimposed on that is a mild S-curve where for a while the slope is decreasing and then it starts increasing

 

Charlie Lineweaver, a top cosmologist (who just had a piece in SciAm BTW) has a picture of that in his survey article "Inflation and the CMB". good article written clearly for general audience but uses math and doesnt oversimplify

 

yeah here's from that stickythread

 

This article by Lineweaver (he was one of the team in charge of COBE

an earlier CMB satellite observatory)

 

"Inflation and the Cosmic Microwave Background"

http://nedwww.ipac.caltech.edu/level5/March03/Lineweaver/Lineweaver_contents.html

 

http://arxiv.org/astro-ph/0305179

 

the second is more legible.

 

LOOK AT FIGURE 14 "the size and destiny of the universe"

http://nedwww.ipac.caltech.edu/level5/March03/Lineweaver/Lineweaver7_7.html

 

this is the picture I wanted. it shows expansion is always going on for 14 billion years but for a while it slows and then it begins to speed up

 

here is figure 14 in more detail

http://nedwww.ipac.caltech.edu/level5/March03/Lineweaver/Figures/figure14.jpg[/quote']

 

Is the Big Bang a Theory or just a Model? I know there is some degree of circumstantial evidence but other than the Cosmic Background Radiation none of it was predicted and the "model" has to changing to fit new data.

More

Curved space is simply a system of measurements made with squidgy units. (E.g., Jello measuring sticks.) That is the trivial secret behind the gaudy curtain of curved space theories. Despite the mighty theatrics, there is nothing behind the curtain but a dishonest little man who refuses to admit that he fudged the units.

 

I have not read and understood where he's coming from but that part cracked me up.

Actually, I am not convinced Mach was wrong, so if you know how to prove he was wrong go for it. .

I'm not convinced Mach was wrong either. I have a butt cheek on each side of that fence. I don't think he had a space-time view of space and time however.

I am curious' date=' but what you say ignores local gravitational field effects of all other bodies in the universe, [b']which matters according to Mach, they contribute to the local gravitational potential[/b], which displaces the CM of the earth-moon system from where it would be if there were no other material in the universe, yes? At any rate...

 

.

I think that, if this is the case, then they "contribute" in such a way as to define

an inertia frame. In other words they all cancel (balance would be a better term because if Mach was right we might all have less inertia) and can be ignored.

 

I guess earth and moon are revolving around a common point which is not exactly the center of the earth. how far is that point (in miles or kilometers or fractions of the earths radius or whatever) from the center of the earth.

 

.

Should be very close to the centre of gravity of the earth/moon system.

The moon is spinning, albeit very slowly.

I was referring to a hypothetical moon. Spin (or tidal effects) would tend to make it non-spherical.

Let's call an E-31 black hole "Olber's Mass". If you look far enough into space, eventually you'll see one!

Was the evidence of the acceleration that the redhift was not "as expected" for the galaxies/clusters viewed at that distance/age?

so you could have one radioactive or unstable nucleus (the element has a half life of 2 day or 24 hours) but yet you have no clue when it will really decay or emit radiation?

You have a "clue". If it has a one day half life it has a 50% chance of decaying in the "next" 24 hours.

If the moon is a perfect sphere it's probably not spinning. If it's spinning anyway there should be an effective weight difference.

If it's orbiting the earth there should be tidal effects making you lighter on the point closest to Earth and also lighter (by almost as much) on the point farthest from Earth.

so far there are only 2 theories of how the universe will 'end'

 

1- The big crunch: the gravity in the universe is so powerful that over-powers the expanding universe and it all comes back to one place and eventually we have a reverse-big-bang

 

2- The Big Freeze: the universe will continue to expand and all stars will eventually burn out and the universe will become dark' date=' frozen, and time will have practically stopped.

 

 

 

do i have this info right? wrong? close? Please add-on or correct this.[/quote']

 

Why will time practically stop?

the assumption is that dark energy density is constant throughout all space and time at a value of about 0.6 joules per cubic kilometer.

 

it stays that density even while space expands! this is why people sometimes refer to it as the cosmological constant.

 

but matter thins out as space expands!

 

therefore 5 billion years ago' date=' when the universe had not expanded so much, matter was much more concentrated and dark energy was relatively insignificant.

the attractive force of matter which slows expansion dominated!

 

up to 5 billion years ago (and people vary about when exactly, maybe changeover was only 1 or 2 billion years ago, but at least 5 billion years ago) was the MATTER DOMINATED period when matter was the dominate percentage of stuff and expansion was slowing.

 

but expansion continued enough so that matter got so thinned out that now dark energy is 73 percent and it dominates!

 

therefore because of the expansive effect of dark energy the expansion is accelerating.

 

Is that enough of an xplanation of the changeover or do you have more questions about it?[/quote']

 

Isn't Dark Matter required as an attractive force within galaxies?

JC what exactly[/b'] is string theory?

I don't know exactly but it's a multi-dimensional (10, 11 or 26?) theory based on 1 dimensional strings many times smaller than the particles we know/don't know so well. Hoped to explain all the known forces.

Newton, Einstein. Maxwell, Galileo in that order

Bohr is top 20 or so which is not too shabby either.

If String Theory sucks does this increase interest in other kaluza-klein theories or put a damper on the whole thing?

All right I have a question.

 

Take a body at rest' date=' and not spinning. Its center of inertia is at rest. So we say that the object isn't accelerating in the frame.

 

[/quote']

 

This is only true if there is no net force on it.

 

What happens when the black hole is smaller than the Schwarzchild radius?

?

Aren't they identical?

first let's both notice that this is purely theoretical' date=' [b']humans have not yet observed a black hole up close[/b] enough to detect its Hawking temperature and its Hawking radiation.

Except Geoffrey, and we all know what happened to him!

Greater uncertainty about whose velocity? Photons travel at c' date=' so there is really no uncertainty about their velocity.

 

If you mean the uncertainty of the target, that'll be tru regardless of the photon properties. If you know the position better, you have more uncertainty in the velocity. The reason you get better position information is that the light is more localized and there is less "smearing" from diffraction.[/quote']

 

Uncertainty of the target particle.

 

Edit: So you get less "smearing" and higher precision for position with a higher frequency/energy photon. Would you therefore get less precision for velocity? (for the targetparticle of course)

Does it matter?

 

I think the lesson of self-interference in the double-slit experiment is that while you can think of it as a photon when you create it and when it interacts with the detection screen' date=' you still have to think of it as a wave if you stick a wave-like measurement in its path.[/quote']

 

I think it would matter if there was a verifiable difference.

 

Apparently there is not (no known difference)?

I have a small (cross section 30" X 20") wind tunnel that is low speed (30 ft/s). For drag I use elastic from inside a bungy cord. I calibrated it and it was not linear (didn't follow Hooke's law) but it was reasonably consistent for crude measurements. For visualization I reach in with a wool tuft "tickler" on a coat hanger.I would like to use smoke at some point.

I'm guessing the extra drag induced by the wing would negate any gas savings.

Good guess, a lot of the drag reduction in recent years has been accomplished by reducing lift.

Longitudinal wave is destructive to a ship in an ocean while transerve is not really much' date=' right?[/quote']

 

In hydrodynamics the "transverse" wave is transverse to and produced by the ship.

 

I think in terms of physics water waves are generally transverse waves as they are mass/gravity waves with the transverse direction being vertical.

 

Sound waves, compression waves, (I think) are longitudinal waves. (correct?)

 

All that being said I think you are correct if you are saying the forward "momentum" is the most destructive. I have some sea containers that are used for storage that were damaged at sea. The sea "punched" the forward ends in as much as 4 feet. (You should see the ones that are unusable even for storage.)

 

However:

Remember the "Edmund Fitzgerald" in the Gordon Lightfoot song? I think it was sunk by the transverse "portion" of the wave/waves. The ship broke up from lack of support (buoyant forces) where a (large) trough coincided with a weakness in the ship.

well' date=' that gives your answer. one at a time produces interference, they interfere with themselves.

 

?[/quote']

 

Now send them billions at a time. Is the primary interference "self interference" or otherwise?

.

 

site note: for light' date=' is the probablility wave for a photon the same wave as the em wave?[/quote']

 

OK, this is a "blurt" so someone correct me who knows better (or confirm it on the off chance that I am right):

 

Photons of different frequencies have different probability waves. Higher frequencies can be used to more accurately probe the positions of particles, with greater uncertainty about their velocity than lower frequencies.